Light emitting elements (light emitting devices) including group III nitrides and having quantum dot structures in light emitting layers are well known (see for example Japanese Patent Application Laid-open No. 2002-368267). Those devices achieve highly efficient emission by dispersing, in a matrix region, island crystals which are so minute as to cause quantum effects and which are doped with a predetermined rare-earth or transition-metal element, and then by using the resultant carrier confinement effect of quantum dots.
The formation of conventional quantum dot structures as disclosed in Japanese Patent Application Laid-Open No. 2002-368267 is done using so-called self-organizing techniques. Those are techniques for achieving quantum dot structures in epitaxial growth processes using well-known growth techniques such as MBE, by constituting the island crystals using a substance which has some difference in lattice constant from the one constituting the matrix region as well as by appropriately controlling the composition, the substrate temperature, the atmosphere, and the like. Those techniques allow easy formation of island crystals which act well as quantum dots, without requiring artificial and direct shape control such as micromachining.
It has been shown that no cracks are generated if a so-called AlN template substrate including an AlN film epitaxially formed on a predetermined single crystal base material is prepared and an AlGaN layer is epitaxially formed on the AlN template substrate by using a MOCVD technique to grow to a thickness of not less than 900 nm (see for example Y. Kida, T. Shibata, H. Miyake, and K. Hirayama “Metalorganic Vapor Phase Epitaxy Growth and Study of Stress in AlGaN Using Epitaxial AlN as Underlying Layer,” Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L572-L574). Such a thickness of 900 nm is a thickness much greater than a critical film thickness of tens of nanometers for crack generation which is theoretically expected.